The Artist's Assistant, In the Study and Practice of Mechanical Sciences: Calculated for the Improvement of Genius. Illustrated with Copper-Plates — Birmingham, [ca. 1785]

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THE ARTIST'S ASSISTANT. 165

and the colour defired ; if while he not in queflion,
which demands a peculiar treatment, as I fhall below
explain ; or great brightnefs be not required, when
alio other means muftbe purfued.

The colours ufed with the fhell-lac varnifh mav
be any pigments whatever, which give the teint of
the ground defired, and they may be mixt together
to form browns or any compound colours ; but, with
refpe£f. to fuch as require peculiar methods for the
producing them of the firft degree of brightnefs, I
fhall particularize th<%n below.

The colours for grounds may otherwife be mixed
with the white varnifhes formed in oil of turpentine ;
but thefe varnifhes have no advantages over the
fhell-lac but in their whitenefs, which preferves the
brightnefs of the colours, and they are at the fame
time greatly inferior in hardnefs to it.

As metals never require to be under coated with
whiting, they may be treated in the fame manner as
wood or leather, when the undercoat is omitted, ex-
cept in the inftances particularly fpoken of below.

Of white japan grounds__The forming a ground

perfectly white, and of the firft degree of hardnefs,
remains hitherto a defideratum, or matter fought for
in the art of japanning. As there are no fubftances
which can be diffolved, fo as to form.a very hard
varnifh, but what have too much colour not to de-
prave the whitenefs when laid on of a due thicknefs
over the work, except fome very late difcoverics not
hitherto brought into praftice.

The neareft approach, however, to a perfeft white
varnifh, by means already known to the public, :s
znade by the following compofition :

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